Investigating different bio-responses of the upper ocean to Typhoon Haitang using Argo and satellite data

Abstract

The responses of the upper ocean to Typhoon Haitang in July 2005 are investigated using Argo float and multiplatform satellite data. The results show decreasing sea surface temperature (SST), a deepening of the mixed layer depth (MLD), and enhanced Chlorophyll-a (Chl-a) concentration. Two extreme cool regions are identified. While the magnitude of SST cooling in the two regions is similar, the biological response (Chl-a enhancement) differs. To facilitate comparisons, the region to the northeast of Taiwan is defined as region A and the region east of Taiwan as region B. Ekman pumping and the intrusion of the Kuroshio play an important role in the enhancement of Chl-a in region A. Cold eddies provide the material source for the formation of the cold center in region B, where mixing is dominant. Because of the relatively high translation speed (5 m/s) in region B, Ekman pumping has little influence on the cooling and Chl-a enhancement processes. Moreover, the MLD is shallower than the nutricline, which means that mixing does not result in a marked increase in nutrients in the euphotic layer (where the nutrient concentration is uniformly depleted). Sea temperatures, in contrast, gradually decrease with depth below the bottom of the mixed layer. In contrast to region A, region B showed no significant enhancement of Chl-a but strong SST cooling.